Check for valid PC when stepping in the ARM sim debugger.
Check for valid PC when stepping in the ARM sim debugger.

BUG=v8:2134
TEST=

Review URL: https://chromiumcodereview.appspot.com/10546169

git-svn-id: b158db1e4b4ab85d4c9e510fdef4b1e8c614b15b@11821 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh